Continuity mistake: At the cocktail party, Ettinger and Bacchus are sitting with their shoulders touching in close-ups, but they're more than a foot apart in all the full shots. (00:07:05)
The Beacon - S1-E26
Plot hole: Barrows introduces himself as "Dr. Dennis Barrows," and Teddy asks, "What's a doctor?" As the isolated villagers have never heard of doctors, Teddy would have no way to know that "Doctor" was a title/profession and not simply part of Barrows' name. He should have asked, "What kind of a name is Doctor?"
I of Newton - S1-E29
Revealing mistake: Set lights are visible in the Demon's sunglasses while he is wearing them and when he is not.
I of Newton - S1-E29
Visible crew/equipment: A boom mic dips into the scene during Sam and the demon's conversation in the classroom.
The Little People of Killany Woods - S1-E34
Visible crew/equipment: When it's opened for Mulvaney, the hardware store's glass-paned door reflects several large, round studio lights. (00:06:05)
Continuity mistake: The pizza crust in Toby's hand keeps changing positions depending on the angle of the camera shot as he talks with Mr. Bendictson.
To See the Invisible Man - S1-E40
Continuity mistake: In the cafeteria, the "invisibility" mark on Mitchell's forehead has moved to a higher spot than it occupied in previous scenes. (00:05:00)
To See the Invisible Man - S1-E40
Visible crew/equipment: When the woman ignores Mitchell and rushes into her apartment building, the glass door she opens reflects the camera, crew and studio lights. (00:06:20)
Tooth and Consequences - S1-E41
Revealing mistake: The glue holding the mustache to actor David Birney's (Dr. Myron Mandel) upper lip is visible.
Other mistake: Veteran actor Elisha Cook's name is misspelled "Elisa Cook" in the opening credits. (00:01:00)
Continuity mistake: The water level in the dispenser rises and falls by itself several times throughout the episode. (00:08:05)
Revealing mistake: In the close-up of Frost's hand while the doctor is stitching up his wound, you can see the delineated edges of the latex make-up patch used to simulate the injury. (00:12:30)
Continuity mistake: In 1912, Ray writes his letter in pencil. When it's delivered to Melissa in 1986, it's written in black ink. (00:20:15)
Time and Teresa Golowitz - S2-E18
Continuity mistake: As they talk, Prince and the pianist stand beside the apartment wall that's covered with Broadway show posters. There's no break in their conversation, but when the shot cuts, they're across the room in front of the window. (00:03:15)
Song of the Younger World - S2-E20
Factual error: It's the 1800s, but Amy's skirt has a 20th Century zipper running down the back. (00:05:15)
Song of the Younger World - S2-E20
Factual error: The 19th Century reformatory has modern electric light bulbs hanging from the corridor ceilings. (00:21:10)
The Crossing - S3-E3
Continuity mistake: Father Cassidy approaches Monsignor Perot and shakes his hand in the front shot, and does it again in the rear shot.
The Hunters - S3-E4
Continuity mistake: Sheriff Roy moves his right hand from the side of his jacket to outstretched twice as he approaches to inspect the sheep's carcass.
The Hunters - S3-E4
Continuity mistake: The shot behind shows Dr.Cline swinging her flashlight to her far right to illuminate the cave drawings. The next shot to her front shows the flashlight straight and centered close to her body.
Answer: Poisoned food, heart attack from eating too much food, or he slipped in the shower. The list is endless.